1. Field of the Invention
The present invention relates to a compact and low-cost DC/AC converter to supply power to a plurality of loads and a controller for the DC/AC converter.
2. Description of the Related Art
An example of a DC/AC converter is disclosed in Japanese Unexamined Patent Application Publication No. 2007-123010. This related art is a discharge lamp lighting apparatus for lighting a discharge lamp such as a cold cathode fluorescent lamp (CCFL). The apparatus controls necessary power for the discharge lamp by monitoring a load current passing through the discharge lamp, and according to the monitored load current, modulating the oscillation frequency of a switching network of an inverter circuit, i.e., a DC/AC converter arranged in the apparatus.
FIG. 1 illustrates the discharge lamp lighting apparatus 1000 according to the above-mentioned related art. The apparatus 1000 includes a DC power source 200, the inverter circuit 300, and a discharge current monitor 400. The oscillation frequency of the inverter circuit 300 is controllable. The inverter circuit 300 receives a DC voltage from the DC power source 200, converts the DC voltage into a high-frequency voltage having the oscillation frequency of the inverter circuit 300, and uses the high-frequency voltage to drive, through a coupling capacitor 105, a load circuit L100. The load circuit L100 includes a series resonant circuit and the discharge lamp 107, the series resonant circuit consisting of a resonant capacitor 108 and a resonant inductor (choke coil) 106, the discharge lamp 107 being connected in parallel with the resonant capacitor 108.
When the inverter circuit 300 oscillates at a predetermined frequency to convert the DC voltage into the high-frequency voltage, the discharge current monitor 400 controls the oscillation frequency of the inverter circuit 300. The discharge current monitor 400 includes a current transformer 109 having an output winding that provides an output according to a discharge current of the discharge lamp 107 and a lighting detector Lop100 to detect the presence and magnitude of the discharge current of the discharge lamp 107 according to the output from the current transformer 109.
In the discharge lamp lighting apparatus of the related art illustrated in FIG. 1, the discharge current monitor 400 monitors a discharge current of the discharge lamp 107, and according to the monitored discharge current, controls the oscillation frequency of the inverter circuit 300 and lights the discharge lamp 107.